retiring backwards, as it always does upon suspicion of peril, not turning round, which the size of its runs does not permit, its tail foremost, until it arrives at some collateral gallery, when its flight is head foremost, as with other creatures. If this fur had been strong, as in the rat, or mouse, in these retreats for life it would have doubly retarded the progress of the creature; first by its resistance, and then acting as a brush, so as to choke up the galleries, by removing the loose earth from the sides and ceilings of the arched ways; thus impeding at least, if not absolutely preventing, retreat; but the softness of the fur obviates both these fatal effects. The construction of the hair and fur of different creatures is very various and beautiful; and if we believe in the beneficence of the All- wise Creator, we must conclude that such peculiar fabrications were resorted to for the purpose of being immediately useful, or as necessary to the condition of the animal. In a mere sketch like this, it would conduct me infinitely beyond my intentions, to enumerate the many varieties of hair that are rendered manifest by the microscope; but three or four may be mentioned. The fur or clothing of the mole is internally composed of collateral bars. In man the hairs have at times a central tube, for the conveyance of medullary matter, as in bones, or some nutriment analogous to it; but in the mole there appears to be no communication with the body of the animal, unless the perspirable matter is conducted alternately from side to side along the bars. The fur of the bat has knots like the rudiments of branches. The hairs of the hamster mouse have a central perforation, apparently uninterrupted throughout their whole length. Some of the caterpillars (callimorpha caja) have spines proceeding from the hair that invests their bodies.[44] All these, and the other various contrivances so manifest in the coverings of animals, are probably designed to convey off the perspirable fluids conducive to health in an appropriate manner; to discharge the superabundant heat, and keep the body temperate in some cases: in others, again, to retard perspiration, and thus augment the warmth, by every possible gradation, or to increase the sensibility and perceptions of the animal. Many instances of these effects and modifications might be advanced, deserving a more extensive consideration.